The present invention relates to the sector of irradiation using electron beams. It further relates to a process for the irradiation of strand-shaped irradiated material, and in particular cable insulation or sheathing capable of cross-linking by radiation, or tubes, hoses, or profile elements capable of cross-linking by radiation, with electron beams impacting transversely to the longitudinal axis of the irradiated material, which impact on the irradiated material from two fixed irradiating devices located at an angle to one another which is other than zero degree, and for preference is a right angle.
It further relates to an irradiating device for the performance of the said process, which comprises first media for the generation of an electron beam, and second media which direct the electron beam form the two irradiating devices onto the bodies which are to be irradiated. Such a process and such a device are known, for example, from the earlier patent application from Applicant, PCT/CH 96/00052.
In the manufacture of cables, the cable sheaths or insulating casing is frequently made of rubber, polyolefins, or other cross-linkable polymers, and cross-linked after the sheathing of the interior of the cable in order to improve the thermal and mechanical stability. The cross-linking can in this case be effected by the addition of chemical ancillary substances, but also by irradiating with energy beams, and electron beams in particular. In the case of radiation-induced cross-linking, the matter involves, inter alia, the attaining of a continuous production process with acceptable expenditure on apparatus, in which cables or other irradiated materials running past the radiation source, such as tubes, hoses, or profile elements, receive uniform irradiation, which on the one hand will result in a uniform and complete cross-linking of all the parts and across the entire circumference of the irradiated material, and, on the other, will not incur any undesirable damage due to excessively high local radiation doses with subsequent electrical disruptive discharges.
Both in the patent specification referred to in the preamble, and in EP-A1-0 037 869, cross-linking induced by electron beam is described, in which the electron beams are directed from two irradiating devices located essentially vertical to one another onto the irradiated material which is to be cross-linked (referred to as xe2x80x9ccross-firingxe2x80x9d) . The cross-firing process has a number of disadvantages, however, in the technical embodiments known hitherto: If, as shown in EP-A1-0 037 869 (FIG. 3), two radiation sources are used with downstream scanners in order to effect the irradiation from both the essentially orthogonal irradiating devices, this implies a considerable expenditure in terms of apparatus, because two vacuum devices, two high-voltage and high-current supplies for the electron beam sources and scanning devices respectively in the scanners, and the pertinent vacuum devices are required. If, by contrast, as is shown in FIG. 1 of PCT/CH 96/00052, the beam is divided from one electron beam source and conducted via separate beam guides to two scanners, which direct the beam in temporal packages onto the irradiated material to be cross-linked from the two irradiating devices, it is at present still not possible to use standard apparatus consisting of source and scanners which is commercially tenable. Rather, special apparatus must be created, which requires considerable expenditure.
The objective of the invention is therefore to provide a process for radiation cross-linking of strand-shaped irradiated material, such as cores, cables, tubes, hoses, profile elements and the like, which can be applied by the use of only slightly modified standard components in a simple manner, and which at the same time is characterised by homogenous irradiation results, as well as an irradiating device for the performance of the said process.
This objective is achieved by a process of the type referred to in the preamble in that a scanned electron beam is created from an electron beam in a scanner by means of a scanning device which creates a radiation fan by means of the temporally-controlled slewing backwards and forwards in a predetermined angle range transversely to the longitudinal direction of the irradiated material, and that the scanned electron beam is deflected by means of a deflector magnet arranged between the scanning device and the irradiated material, for each scanning angle of the radiation field, in such a way that it impinges on the irradiated material which is to be treated from one of the two fixed irradiation devices. The core of the invention lies in the fact that the scanned electron beam, scanned transversely to the longitudinal direction of the irradiated material by means of additional deflection, optionally into the two desired irradiation directions. In this way it is possible, with one single standard piece of apparatus, consisting of electron beam source and scanner, and with only one additional deflection device, to achieve the cross-firing process simply and economically.
In principle, it is conceivable that a permanent magnet or an electromagnet operated with a constant magnetic current can be used as the deflection magnet. The deflection magnet must then provide differing magnetic field strengths and directions at different places along the direction of the scan, in order that, depending on the scan angle, it is possible to achieve deflection of differing strengths, moving in different directions, of the scanned electron beam in the deflection magnet. This means, however, a relatively complex layout of the deflection magnet, which can only be adjusted with difficulty if changes are effected in the beam system.
A preferred embodiment of the process according to the invention is therefore characterised in that a controllable electromagnet is used as the deflection magnet, which in the area of the fan-shaped radiation field creates an essentially homogenous magnetic field of controllable magnetic field strength and direction, and that the magnetic field strength and direction are changed synchronously to the deflection of the electron beam in the scan direction of the scanner in such a way that the electron beam deflected in the magnetic field of the deflection magnet impinges on the irradiated material from one of the two irradiation devices. The homogenous magnetic field can be created relatively simply. By the temporal control of the magnetic field strength, it is easily possible, with electronic media, at any time, which simultaneously determines a specific scan angle for the scanned electron beam, at which the beam runs through the scanner, an appropriate deflection angle can be attained in the deflection magnet. If the parameters in the electron source or in the scanner change, the device can be readjusted by simple adaptations in the control device.
For preference, the scanning device in the scanner deflects the electron beam with a scan frequency fHd s, and the deflection magnet alters the magnetic field with a magnetic field frequency fB, which is greater, smaller, or equal to the scan frequency fs; i.e. the function fB=k.fs, applies, with k as any desired number other than zero.
According to a first further embodiment, fB=fs, and when the scanned electron beam is slewed away, it is deflected into one irradiation direction, and when it is slewed back it is deflected into the other irradiation direction. As a result, the irradiated material is irradiated from both irradiation directions in each scan period.
A further development of this embodiment is characterised by fB=fs/n where n=2,3,4, . . . , and that the scanned electron beam in n-times slewing backwards and forwards of the scanned electron beam is deflected in each case in one irradiation direction and, in the subsequent n-times slewing backwards and forwards, is deflected in the other irradiation direction.
A further preferred embodiment of the process according to the invention is characterised in that the irradiated material is moved in the longitudinal direction relative to the scanner at a speed v, that the beam fan created by the scanner, measured at the height of the irradiated material and in the longitudinal direction of the irradiated material, featured a width W, and that the deflection magnet is operated at a minimum magnetic field frequency fBmin, which satisfies the equation fBmin =v/W.
The irradiation device according to the invention for the performance of the process is characterised in that the second media comprises a scanner arranged essentially transverse to the longitudinal direction of the irradiated material, and a deflection magnet for deflecting the scanned electron beam.
A preferred embodiment of the device according to the invention is characterised in that the deflection magnet is an electromagnet capable of being controlled in terms of magnetic field strength and direction, which creates an essentially homogenous magnetic field for the deflection of the scanned electron beam, that actuation media are provided for the deflection magnet, which control the magnetic field strength and direction of the deflection magnet in such a way that the electron beam deflected by the deflection magnet always impinges on the material to be irradiated from one of the two irradiation devices, that the scanner comprises a scan device which is actuated with a scan frequency fs, created in an oscillator, that the actuation media for synchronisation stand in an operational connection with the oscillator, and that the actuation media comprise a frequency divider and a function generator. With the aid of the frequency divider, switchover between the irradiation directions can be effected at a frequency which is only a fraction of the scan frequency. The function generator allows for the precise control of the temporal sequence of the magnetic field in the deflection magnet.
Further embodiments can be derived from the dependent claims.